Chemo- and Regio-selectivity in the TiO2 mediated photooxidation of 1,n-diols

Proper reaction conditions have been found for the conversion of 1,2 propanediol, 1,3 butanediol and 1,4 pentanediol to the corresponding hydroxy-carbonylic compounds with good chemo- and regio-selectivity by photochemical excitation of CH2Cl2 suspensions of TiO2. In particular, about 90% of hydroxyacetone from 1,2 propanediol and more than 75% of 4-hydroxypentanal from 1,4 pentandiol could be obtained. A remarkable conclusion is that the TiO2-assisted photooxidation of 1,4-pentanediol is carried out with good selectivity to 4-hydroxypentanal and low mineralization to CO2 also under high conversion conditions. The adsorption of the diol on the semiconductor is an important parameter able to affect efficiency and selectivity of the photocatalytic process. In particular, the high polarity of the TiO2 surface favours the preferential adsorption of the primary OH group of the diol molecule, thus favouring its subsequent oxidation.